There are several tracking arrangements for tracking a moving object, such as a hunting dog. A dog can be equipped with for example a radio transmitter, the analogue signal transmitted by which is tracked with a suitable directional antenna. With this arrangement, the direction of the dog is discovered and, based on the strength of the received signal, an estimate, however not very precise, can be made as to how far the dog is with its radio transmitter.
Also a tracking solution is known in which satellite-based GPS (Global Positioning System) positioning and some other wireless digital data transmission network, for example GSM (Global System for Mobile communications) network, is used. An example of such system is shown in FIG. 1a. In the example of FIG. 1a, at least a device 12 carried by an object 11a to be tracked contains a GPS locator. The transmitter contained in the device 12, carried by the object 11a to be tracked, sends the result of the positioning made by means of the GPS either as an SMS (Short Message Service) message or as a data call to a wireless terminal 13 of the tracker through a digital data transmission network 10, reference numerals 12a, 100 and 13a. The used data transmission network can for example be a GSM network. A tracker's terminal 13 may also use a map base representing the area, whereby the position of the dog to be tracked can be expressed on said map.
The system of FIG. 1a can also work for example on a request basis whereby the tracker's terminal 13 sends a request for positioning to the device 12 of the object 11a to be tracked. The device 12 carried by the object 11a to be tracked replies to it by means of an SMS message containing the GPS positioning information.
This arrangement is not entirely real-time, but instead, the tracker can use either the result of a previous positioning or else the tracker will have to perform a new positioning which takes time and increases tracking costs, since every sent SMS message costs money. Additionally, with one SMS message, the position information can be transmitted only to one tracker's terminal 13. If several persons wish to track the object 11a with their own terminals, a system has to be created wherein the device 12 of the object 11a being tracked sends a separate SMS message to each terminal.
If the positioning information is wished to be transmitted to several tracking devices simultaneously, either a separate SMS message has to be sent to each tracking device or a data call connection has to be established. The SMS messages are always charged on the basis of sent messages.
Thus, such tracking arrangement is rather expensive, since the price defined by the operator for messages to be transmitted has to be paid for each positioning information sent.
FIG. 1b describes a solution wherein a device 14 carried by an object 11a to be tracked uses GPS positioning. The device 14 of the object to be tracked 11a sends the positioning result by means of a radio transmitter as an RF transmission 15a directly to the tracker's device 15. The connection can be established for example as a radio link using a so-called FRS (Family Radio Service) service. In the FRS service, the data is transmitted using an FM modulated carrier wave on UHF (Ultra High Frequency) frequency. The used radio phone is a kind of “Walkie talkie” radio phone. The number of channels is limited in the FRS15 service, and also the range of the radio communication is in practice limited to less than 3 km.
In this system, distribution of the telematic data to the terminals located outside the range becomes problematic.
Also tracking solutions are known in which a device 12 carried by an object to be tracked can connect also to a packet switched cellular network, for example a GPRS (General Packet Radio Service) network. In such system, the telematic data measured by the device 12 is sent to a server wherefrom it can be sent reasonably in real time to the tracker's device. Furthermore, the positioning information can be sent from the server to an unlimited number of trackers' devices through said packet switched network.
Although GPRS based solutions are becoming more and more common, users have a large number of devices in which the only data transmission possibility is a text message or a circuit switched data call that are sent by means of a point-to-point radio connection. In these systems, the sending device, for example a locator, has to send the telematic data to each receiver separately. This incurs additional costs and increases current consumption.
In the RF based transmission path, the telematic data cannot be transmitted to the receivers outside the radio range, and additionally, each receiver must contain a radio unit that may be even rather rare.
Also tracking solutions are known in which the device being tracked send its telematic data directly to a server by means of a text message, wherefrom the server forwards the telematic data by means of packet data to the viewing terminals. In these arrangements, the extensive cost of SMS gateway services becomes problematic. The owner of the server has to pay for each incoming message. Alternatively, a text message receiving modem can be connected to the server. In this case, the limited performance of the modem forms a problem. It cannot receive messages arriving constantly from a large number of devices. In the existent text message based solutions, the position information reply is sent to the requester. In this case, the server should request for a position by means of a text message from the locator on the object to be tracked, whereby the message cost would double.
It is an object of the invention to present a method and an arrangement with which the telematic data of an object to be tracked can be distributed cost-effectively with more trackers also in regard to the devices to be tracked that cannot connect to a packet switched radio network.